Air strikes by US-led coalition forces in Syria have killed or wounded many civilians, indicating that required precautions were ignored and war crimes may have been committed, United Nations investigators said on Wednesday.

Syrian government and allied Russian warplanes are also conducting a deadly campaign that appears to target medical facilities, schools, markets and farmland and which may also amount to war crimes, the report by the UN Commission of Inquiry on Syria said.

The investigators also accused Hay'at Tahrir al-Sham, the militant alliance that is the dominant armed group in Idlib, of firing rockets indiscriminately and killing civilians.

The report covers the year to July and is based on nearly 300 interviews and analysis of satellite imagery, photographs and videos.

'Indiscriminate attacks'

Backed by US-led coalition air power in a fight to oust the Islamic State group (IS), the Syrian Democratic Forces (SDF) militia retook the miltiant group's last major stronghold of Hajin in eastern Syria in late December.

The coalition's Al-Jazeera Storm operation resulted in a high number of civilian casualties, including in a series of strikes on 3 January in Shafah, south of Hajin, that killed 16 civilians, including 12 children, the UN report said.

"The Commission finds that there are reasonable grounds to believe that international coalition forces may not have directed their attacks at a specific military objective, or failed to do so with the necessary precaution," it said.

"Launching indiscriminate attacks that result in death or injury to civilians amounts to a war crime in cases in which such attacks are conducted recklessly."

Coalition officials could not be reached immediately for comment on the report, the Reuters news agency said.

Night raids by SDF forces backed by coalition helicopter gunships killed and wounded civilians in Shahil and other parts of Deir al-Zor province, in further apparent violations of international law, the investigators said.

Four families 'wiped out in an instant'

In April, a joint report by the Airwars monitoring group and Amnesty International said the US-led coalition was responsible for the deaths of at least 1,600 civilians during its bombardment against IS in Raqaa in 2017.

The report noted one incident where four families had been "wiped out in an instant" after the US-led coalition bombed a Raqqa neighbourhood on 25 September, 2017.

Throughout their investigations, Airwars and Amnesty said they regularly submitted evidence of civilian deaths to the US-led coalition.

This prompted the coalition, comprised of US, British and French armed forces, among others, to admit responsibility for killing 159 civilians.

However, the military alliance dismissed the remainder of deaths reported as "non-credible".

'Intentionally attacking medical personnel'

Wednesday's UN report said Syrian government forces carried out repeated air strikes in Saraqib, in northwest Idlib province on 9 March, damaging Al-Hayat women's and children's hospital, despite pro-government forces being aware of its coordinates.

Syria: At least 1,600 civilians killed by US coalition in Raqqa, probe finds